Juppe said France considers Burhan Ghaliun's Syrian National Council a "legitimate interlocutor" and said he would take to Brussels the idea of escape routes for Syrian civilians fleeing Bashar al-Assad's forces.

"We examined the question of humanitarian corridors and I will ask the next meeting of the European Council to put this point on its agenda," Juppe said.

"If there could be a humanitarian dimension to the zones, which could be secured, to protect the population, that's a question that must be studied with the European Union and the Arab League."

There have been reports that Turkey and NATO allies such as France are considering imposing a no-fly zone and a buffer zone on Syrian territory to give the opposition breathing space while it organises its revolt.

No official source has gone this far, however, and Juppe's statement was the first sign that something of the sort might be envisaged.

"The Syrian National Council is the legitimate interlocutor, and we will continue to work with it," Juppe said, stopping short of formally recognising the body and stressing that it must be inclusive.

"We are working on a formal recognition with the Arab League and all of our allies," Juppe said.

The SNC headed by Paris-based Ghaliun is one of at least four Syrian opposition movements, but is seen as the most representative and claims to speak for activists both inside and outside the country.

Speaking to reporters after the joint news conference, Ghaliun said the SNC did not want to see the fledgling Free Syrian Army, an armed rebel group, take the fight directly to the regime's far superior forces.

"We would like this army to carry out defensive actions to protect those who have left the (regime's) army and peaceful demonstrations, but not take on offensive actions against the army," he said.

In recent weeks there have been increasing reports that a rebel army has begun fighting Assad's regime in parallel to a largely peaceful street revolt that has faced brutal repression from regular forces.

This has increased fears the nine-month old revolt against the regime is slipping towards civil war. Four more civilians were killed on Wednesday, in a conflict which the United Nations says has claimed more than 3,500 lives.

Syria's northern neighbour Turkey warned, meanwhile, that the crisis was at "the point of no return" amid a growing chorus of international anger over the eight-month crackdown on dissent.